Various hybrid powertrain architectures are known for managing the input and output torques of various prime-movers in hybrid vehicles, most commonly internal combustion engines and electric machines. Series hybrid architectures are generally characterized by an internal combustion engine driving an electric generator which in turn provides electrical power to an electric drivetrain and to a battery pack. The internal combustion engine in a series hybrid is not directly mechanically coupled to the drivetrain. The electric generator may also operate in a motoring mode to provide a starting function to the internal combustion engine, and the electric drivetrain may recapture vehicle braking energy by also operating in a generator mode to recharge the battery pack. Parallel hybrid architectures are generally characterized by an internal combustion engine and an electric motor which both have a direct mechanical coupling to the drivetrain. The drivetrain conventionally includes a shifting transmission to provide the necessary gear ratios for wide range operation.
Electrically variable transmissions (EVT) are known which provide for continuously variable speed ratios by combining features from both series and parallel hybrid powertrain architectures. EVTs are operable with a direct mechanical path between an internal combustion engine and a final drive unit thus enabling high transmission efficiency and application of lower cost and less massive motor hardware. EVTs are also operable with engine operation mechanically independent from the final drive or in various mechanical/electrical split contributions thereby enabling high-torque continuously variable speed ratios, electrically dominated launches, regenerative braking, engine off idling, and multi-mode operation.
It is known to select engine power from the road-load power required plus an additional quantity of engine power based on the energy storage system's (e.g. battery's) state-of-charge. Following selection of engine power, the engine's optimal fuel economy or optimal emissions map or a combination thereof may be used to select the engine's torque/speed operating point. The battery power effected is that which is required, in combination with the engine power, to meet the road-load power requirements and to compensate for power losses within the system.
Known systems do not optimize the power flow of all the propulsion system components. Typically, only the engine operation is optimized. The prior art does not weigh additional factors such as other system mechanical and electrical losses and battery usage factors in selecting the overall system's preferred operating point.